An arrhythmia is a medical condition in which there exists a problem with the rate or rhythm of the heartbeat usually due to abnormal electrical activity in the heart. More specific types of arrhythmia include when the heart beats too fast (known as tachycardia), too slow (known as bradycardia) or with an irregular rhythm (known as cardiac fibrillation). Two general devices are known in the art for helping people who experience arrhythmias. One is known as a pacemaker, the other is known as an implantable cardioverter defibrillator (herein abbreviated ICD). Pacemakers are implantable devices which continuously measure the heartbeat and electrical activity in the heart. Pacemakers can detect irregularities in the heartbeat, i.e. arrhythmias, and are programmed to provide electrical signals to the heart to restore its normal beating rhythm.
Reference is now made to FIG. 1, which is a schematic illustration of a pacemaker implanted in a patient, generally referenced 10, as is known in the art. As shown in FIG. 1, a pacemaker 12 is implanted in a patient 14, having a heart 16 and a ribcage 18. Pacemaker includes two main components, a can 20 and electrical leads 22. Can 20 includes a power source (not shown), such as a battery, as well as an electronic device (not shown) for monitoring the electrical activity in the heart and for providing electrical signals to the heart when aberrant rhythms of the heart are detected. Can 20 is usually implanted in patient 14 via a surgical procedure on his left side adjacent to and below the clavicle bone (also known as the collarbone), as shown by an arrow 24 in FIG. 1. Electrical leads 22 are coupled with the electronic device in can 20 at one end and are coupled with heart 16 at the other end, the electrical leads being inserted through the subclavian vein (not shown) and the vena cava (not shown). Electrical leads 22 are typically implanted in patient 14 by inserting them percutaneously through his vena cava (not shown). Once attached to heart 16, they are coupled with can 20. Electrical leads 22 are usually flexible and provide electrical signals of heart 16 to the electronic device in can 20 as well as providing electrical signals from the electronic device to heart 16. Typically, electrical leads 22 are implanted in right ventricle 26 and right atrium 28 of heart 16.
ICDs are similar to pacemakers and include similar components, such as a can and electrical leads; thus pacemaker 12 in FIG. 1 could also be an ICD. An ICD differs slightly from a pacemaker in that its can includes a power source, electronics, electrical leads as well as at least one capacitor. The difference between an ICD and a pacemaker is that an ICD can deliver a high voltage electric shock to the heart to terminate an otherwise potentially fatal cardiac tachyarrhythmia. A pacemaker is generally limited to treating bradyarrhythmias which can be treated with a significantly lower voltage electric impulse. The presence of at least one capacitor in an ICD accounts for its difference in function from a pacemaker as the at least one capacitor enables a significantly higher electrical shock to be built up and delivered to the heart. An additional function of an ICD is to send the heart an electrical shock in case of ventricular fibrillation (herein abbreviated VF) and in order to prevent cardiac arrest, i.e., aborted sudden death. The electrical energy required for the electrical shock is built up and stored in the at least one capacitor. ICDs exist as standalone devices yet are also manufactured having the functionality of a pacemaker. In addition, cardiac resynchronization therapy defibrillators (herein abbreviated as CRT-D) include a third electrode allowing for simultaneous pacing of both the right and left ventricles of the heart.
As mentioned above, ICDs, similar to pacemakers, constantly monitor the rate and rhythm of the heart and deliver therapies to the heart by way of an electrical shock. In the case of an ICD, electrical shocks are provided to the heart when the measured electrical activity of the heart exceeds a preset number. State of the art ICDs can distinguish different types of aberrant electrical activity in the heart, such as VF, when the heart contracts irregularly, versus ventricular tachycardia (herein abbreviated VT), when the heart beats regularly but significantly faster than normal. In the case of VT, such ICDs may send electrical signals to the heart to try and pace the heart faster than its intrinsic heart rate in an attempt to stop the tachycardia before it progresses to VF. This technique is known in the art as fast-pacing, overdrive pacing or anti-tachycardia pacing (herein abbreviated ATP). As is known to workers skilled in the art, ATP is only effective if the underlying rhythm of the heart is ventricular tachycardia. ATP is never effective if the heart is already experiencing ventricular fibrillation and thus lacks a consistent heart rate. State of the art ICDs use a combination of various methods to determine if received electrical signals from the electrical leads represent a normal rhythm of the heart, ventricular tachycardia or ventricular fibrillation. It is noted that the placement of an ICD in the body of a patient is similar to that of a pacemaker, however in the case of a CRT-D device, the electrical leads can also be implanted in the left side of the heart via the coronary sinus (not shown) of the heart. This is shown in FIG. 1 as an electrical lead 30, denoted by a dashed line. In addition, is it noted that state of the art ICDs exist in which the electrical leads of an ICD are not inserted into the heart but are positioned subcutaneously above the heart. Such ICDs provide improved safety to a patient since the insertion of the electrical leads of the ICD does not involve any intervention with the heart.
ICDs and pacemakers are known in the art. Major manufacturers of these devices include Medtronic, Boston Scientific, St. Jude Medical, Cameron Health (recently acquired by Boston Scientific), Biotronic and Sorin Group. For example, U.S. Pat. No. 7,363,083 to Bardy et al., assigned to Cameron Health, entitled “Flexible subcutaneous implantable cardioverter-defibrillator” is directed to an implantable cardioverter-defibrillator for subcutaneous positioning over a patient's ribcage. The implantable cardioverter-defibrillator includes a housing which conforms to the patient's ribcage when subcutaneously positioned, an electrode disposed upon a portion of the housing and an electrical circuit located within the housing. The electrical circuit is electrically coupled to the electrode. The implantable cardioverter-defibrillator also includes a battery and a capacitor. The electrical circuitry is configured to detect an abnormal heart rhythm, to charge the capacitor, and to discharge the capacitor to provide a cardioversion/defibrillation shock to the heart. According to another embodiment, the cardioverter-defibrillator also includes a first structural portion for supporting a first cardioversion/defibrillation electrode, which is adapted to be implanted at a first subcutaneous implantation site about the patient's thorax and is also adapted to direct the first cardioversion/defibrillation electrode towards the patient's heart. The cardioverter-defibrillator also includes a second cardioversion/defibrillation electrode, which is adapted to be implanted at a second subcutaneous implantation site about the patient's thorax and is adapted to direct the second cardioversion/defibrillation electrode towards the patient's heart. A connecting structure includes one or more conductors for connecting the first and second structural portions together. The components of the implantable cardioverter/defibrillator are distributed between the first and second structural portions. The components may also be distributed between the one or more conductors of the connecting structure. The plurality of components is interconnected to enable the generation and delivery of cardioversion/defibrillation shocks between the first and second cardioversion/defibrillation electrodes. It is noted that in this patent, the electrodes are implanted subcutaneously however a can is still used to hold the battery, capacitor and electrical circuitry. The can is also used as a contact point for the cardioverter-defibrillator.
U.S. Pat. No. 7,684,864 to Olson et al., assigned to Medtronic, entitled “Subcutaneous cardioverter-defibrillator” is directed to a subcutaneous implantable cardioverter-defibrillator (ICD) which is entirely implantable subcutaneously with minimal surgical intrusion into the body of a patient. The ICD provides distributed cardioversion-defibrillation sense and stimulation electrodes for delivery of cardioversion-defibrillation shock and pacing therapies across the heart when necessary. In one configuration, a hermetically sealed housing is included with one or optionally two subcutaneous sensing and cardioversion-defibrillation therapy delivery leads. In another configuration, two hermetically sealed housings interconnected by a power/signal cable are provided. The housings are generally dynamically configurable to adjust to varying rib structure and associated articulation of the thoracic cavity and muscles. The housings may optionally be flexibly adjusted for ease of implant and patient comfort. In one embodiment, the ICD is electrically coupled to one or more elongated, coil-type high voltage electrodes with the electrodes disposed in a location providing defibrillation vectors covering adequate mass of myocardial tissue to achieve defibrillation and deliver pacing therapy. In another embodiment, more than one high voltage electrode is implemented with the ICD and is connected to all the electrodes. The one or more high voltage electrodes may include a set of coil electrodes disposed in an orientation relative to a patient's heart that provides several different therapy delivery vectors there between. Other state of the art ICDs are described in the following patents: U.S. Pat. Nos. 6,647,292, 7,069,075, 7,835,790 and 8,135,459, all assigned to Cameron Health, U.S. Pat. No. 5,573,551, assigned to Intermedics, U.S. Pat. No. 8,147,486, assigned to St. Jude Medical, U.S. Pat. No. 5,314,451, assigned to Medtronic, and U.S. Pat. No. 7,937,148, assigned to Nanostim.